1. Field of the Invention
The present invention relates to a method for manufacturing a composite high voltage insulator in which a plurality of skirts are manufactured and joined to a rod, and more particularly to a method for manufacturing a composite high voltage insulator in which an expanding pipe is inserted into a plurality of skirts arranged in a line by a skirt holder to expand the inner diameters of the skirts, so that the skirts reach precise positions of the rod, and an adhesive agent is easily applied, so that an interface between different materials is not formed in order to improve reliability of insulator products.
2. Description of the Related Art
Generally, insulators are used to simultaneously insulate and mechanically maintain or support power transmission lines or naked wires of electric equipment, and include a plurality of bellows to achieve sufficient dielectric strength in order to increase the distance thereof per surface area. These bellows prevent the deterioration of the dielectric strength of the insulator, when the surface of the insulator is wet, particularly when salt content or dust is attached to the surface of the insulator.
The above insulators are divided according to application into suspension insulators used in power transmission lines, long-rod insulators, fog-type insulators used to withstand typhoon-force winds, pin insulators used in distribution lines, knob insulators used in interior wirings, insulating tubes, cleat insulators, and support insulators used in circuit breakers or arresters.
FIG. 1 is a sectional view of a conventional composite insulator.
The conventional composite insulator 20 comprises a sheath portion 22 formed on the outer surface of a core rod 10 made of FRP by covering the core rod 10 with a material having a high resistance to environments, such as air pollution or ultraviolet rays, for providing mechanical stress, and skirt portions 24 including sheds formed integrally with the sheath portion 22.
FIG. 2 is an exploded sectional view of the conventional composite insulator illustrating a modular-type method for manufacturing the conventional composite insulator.
The length of composite insulators used in superhigh-voltage lines increases in direction proportion to increase in service voltage. The increased length of the composite insulator generates various problems in a process for manufacturing the composite insulator.
A method for manufacturing the composite high voltage insulator by injection molding once does not form an interface between different materials, thus producing the most reliable product. However, since the composite high voltage insulator has a length of 3˜7 m, it is difficult to solve the warpage of the rod 30, and since a mold corresponding to the length of the composite insulator and a large-volume catapult are essentially required, initial costs are increased.
In order to solve the above problems, a modular method, in which a sheath 34 and skirts 40 are separately molded and are then assembled and attached, has been proposed. In the above modular method for manufacturing a composite high voltage insulator, the sheath 34 and the skirts 40 are separately molded, the sheath 34 is inserted into holes formed through the skirts 40, and an adhesive agent is applied to an interface between the sheath 34 and the skirts 40 to attach the sheath 34 and the skirts 40.
The above conventional method for manufacturing a composite high voltage insulator is divided into two approaches. The first approach is where an adhesive agent is applied to the outer surface of the rod 30 covered with the sheath 34 and the rod 30 is inserted into the holes of the skirts 40 such that the skirts 40 slide towards the inside of the rod 30 using the lubricating function of the adhesive agent In this approach, when the inner diameters of the skirts 40 are excessively small, the adhesive agent applied to the rod 30 covered with the sheath 34 is peeled off by inserting the rod 30 into the holes of the skirts 20. Accordingly, it is difficult to uniformly apply the adhesive agent to the overall surface of the rod 30.
Further, when the inner diameters of the skirts 40 are excessively large, it is easy to insert the rod 30 into the holes of the skirts 40. However, in this case, adhesive characteristics caused due to the compressive force of the skirts 40 are not obtained, and an air layer may be formed in the interface between the skirts 40 and the sheath 34 after the manufacture of the insulator is completed. The above approach is disadvantageous in that the exposed adhesive agent generates an interface between difference materials, the above interface is a weak point of the composite insulator requiring the reliability, and the adhesive agent must have improved resistance to tracking and weather so that the composite insulator is proper to be used outdoors.
The second approach is that an adhesive agent is applied only to the inner walls of the holes of the skirts 40 or is applied to the surface of the rod 30 covered with the sheath 34 to be inserted into the holes of the skirts 40 so that the skirts 40 are attached to the rod 30 using the adhesive agent by inserting the rod 30 into the holes of the skirts 40 under the condition that the holes of the skirts 40 are expanded and then by releasing the expanded state of the holes of the skirts 40. However, this approach is disadvantageous in that it is difficult to expand the holes of the skirts 40 due to the general shapes of the skirts 40 and characteristics of materials of the skirts 40.